The basic method for providing fins on a tube is by a forming roll rotating against the surface of the tube. A tubular work piece on the tube external surfaces is caused to flow by plastic deformation to form upstanding spiral fins. Machines for accomplishing this method are well-known in the industry and commonly commercially available—that is, each finned tube has a continuous spiral fin formed on its exterior surface. Tubes having spirally formed fins are commonly used in the construction of heat exchangers.
A prior issued patent that illustrates methods of forming spiral fins on a tube is U.S. Pat. No.5,003,690 issued on Apr. 2,1991 entitled FINNING AND THREAD ROLLING MACHINE. Other patents showing the construction of spirally wound fins on tubular members include the following:
PATENTNUMBERINVENTOR(S)TITLE4,612,791Przbyla, et al.Method and Apparatus for RollingTransversely Ribbed Bimetallic Pipes5,146,979ZohlerEnhanced Heat Transfer Surface andApparatus and Method of Manufacture5,222,299ZohlerEnhanced Heat Transfer Surface andApparatus and Method of Manufacture5,803,164Schuez, et al.Multiple Finned Tube and a Method for itsManufacture5,916,318AndersonMachine for Simultaneously FormingThreads or Fins on MultipleCylindrical Work pieces
By and large each of these references teach a method and/or machine for producing an integral fin tube in which the fin is spiraled. Typically, a spiraled fin is formed on an elongated tubular member by rotating the tubular member against one or more forming rolls that are supported by arbors capably of being adjustably positioned inwardly and outwardly radially from the work piece. Rotary motion is applied to one or more forming rolls to cause the work piece to also rotate as fins are formed by metal displacement on the exterior of the work piece.
In each case, the formed fin is an elongated spiral. The invention herein is, in contrast with these prior art references, concerned not with the production of a spiral fin, but with the production of radial fins. By “radial fins” it is meant a sequence of closely spaced, paralleled fins where each fin is a complete, uninterrupted circular portion extending in a radial plane of the axis of a tubular member.
Air flowing through a heat exchanger having tubes with parallel fins undergoes reduced pressure drop compared to a heat exchanger of the same size and capacity wherein the fins are spiraled.